Multiple target tracker and liquid crystal waveguide (lcwg) beam steerer for designation, range finding and active imaging

ABSTRACT

A multiple target tracker and beam steerer utilizes liquid crystal waveguide (LCWG) beam steering to illuminate multiple tracked targets per frame one target at a time for designation, range finding or active imaging. The steering rate and range afforded by the LCWG supports various tracker configurations (out-of-band, in-band or dual-band video cameras), LADAR detectors (single pixel or pixelated) and prioritization of tracked targets to vary the revisit rate or dwell time for an illuminated target. A user interface accepts commands from an operator to select the targeting mode, control cue-box size and position within the FOV and target selection.

CROSS-REFERENCES TO RELATED APPLICATION

This application is a continuation and claims benefit under 35 U.S.C.Section 120 to the following co-pending U.S. patent application Ser. No.14/864151 filed on Sep. 24, 2015, entitled MULTIPLE TARGET TRACKER ANDLIQUID CRYSTAL WAVEGUIDE (LCWG) BEAM STEERER FOR DESIGNATION, RANGEFINDING AND ACTIVE IMAGING and incorporates its entire disclosure byreference.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to target tracking and laser beam steering toilluminate the tracked targets for designation, range finding or activeimaging, and more particularly to tracking and illumination of multipletargets per frame, one target at a time in a field-of-view (FOV).

Description of the Related Art

Laser beam steering is used to perform functions such as Designation,Range Finding and Active Imaging. Typically, a laser is configured totransmit a laser beam, typically pulsed, along a fixed transmission path(“along boresight”). The laser may be steered manually in a hand-heldunit or automatically on a gimbal mounted system to point boresight atthe target.

Laser Designation transmits an encoded pulsed laser beam at a wavelengthof 1,064 nm to designate a target. The pulsed laser beam has a pulserepetition frequency (PRF) in which a defined pattern of pulses forms adesignation code. Laser Designation of targets is used duringacquisition, tracking and terminal guidance of guided munitions with asensor commonly known as a semi-active laser (SAL) sensor.

Laser range finders transmit laser beams at a remote target to determinethe distance or range to the remote target. Laser range findersgenerally operate on the “time of flight” principle by measuring thetime taken for a laser pulse to travel to the target and be reflectedback to the range finder. With the speed of the laser light being aknown value, and with an accurate measurement of the time taken for thelaser light to travel to the target and back to the range finder, therange finder is able to calculate the distance from the range finder tothe target. Other techniques such as continuous wave (CW) or frequencymodulated (FM) modulated CW may be used to determine range. An“eye-safe” wavelength of 1,550 nm is typical although 1,064 nm or otherwavelengths may be used as well.

Active imaging detects laser energy reflected by elements within a sceneto form an image of the scene. The active image of a portion of thescene may augment a passive image of the entire scene. Active imagingprovides a measurably higher signal-to-noise ratio (SNR) than passiveimaging, Which can be useful for target detection, acquisition,classification or aimpoint selection.

U.S. Pat. No. 8,400,619 entitled “Systems and methods for automatictarget tracking and beam steering” employs an image capturing system foracquiring a series of images in real time of a distant area containing aremote target, and a processing system for processing the acquiredimages to identify the target and follow its position across the seriesof images. An automatic beam steering system and method operate inconjunction with a laser source for emitting a laser beam to betransmitted in the form of a transmitted laser beam extending along asteerable beam transmission axis to the remote target. The beam steeringsystem is controlled by the processing system to steer the beamtransmission axis to be aimed at the target being tracked by the targettracking system, so that the transmitted laser beam will be transmittedat the appropriate angle and in the appropriate direction to be aimed atthe tracked target. “The beam steering system may accomplish steering ofthe beam transmission axis by decentering or adjusting the position ofone or more components of an optical system, . . . ” (Col. 7, lines6-14). This approach allows for small steering deviations off ofboresight to designate a single tracked target.

The image processing system 34 controls the beam steering system 11 tocompensate for positional changes of the target 26 by continuouslyadjusting the position of the laser source 15 as needed for the angleand direction of the beam transmission axis 25 to be aimed at the target26 being tracked via the target tracking software 68. “Positionalchanges of the target may result from extraneous movement of theoperator and/or movement of the target as discussed hereinabove.” (Col14, lines 1.-6), “The target tracking and beam steering processes areperformed very rapidly, with images typically being processed within thetime it takes for the next frame to be received, such that the targettracking system 10 will normally “lock” on the target and the rangefinder 12 will be ready for range acquisition very quickly after theoperator has appropriately directed the forward or pointing end of thetransmission system 14 toward the target 26. Once the target 26 is“locked”, activation of the range finder 12 to emit the laser beam 23from the laser source 15 will result in the transmitted laser beam 24being transmitted accurately to the target 26.” Col 14, lines 44-54. Inlay terms, the operator points the weapon at the target, the imagecapture system determines a small correction to point the laserprecisely at the target, the beam steering system mechanically moves theoptical component to make the correction and once “locked”, the operatorpulls the trigger to transmit the laser beam towards the single target.This method simply corrects the aimpoint for a single target.

Another class of problems involves tracking and illuminating multipletargets within a field-of-view (FOV) about boresight. An image capturesystem generates a list of tracked targets and angles-to-targets at theframe rate of the imaging system. One approach is to mechanically steera laser spot-beam to illuminate different targets. Mechanical steeringhas size, weight, power and cost (SWaP-C) limitations that limit itseffectiveness, especially for small platforms. Speed constraints limitthe ability to illuminate multiple targets per frame within a FOV.Another approach is to non-mechanically steer a laser spot beam usingoptical phased arrays in combination with polarization gratings. Thisapproach has a lower SWaP-C than mechanical beam steering but has alimited ability to illuminate multiple targets within a FOV.

The current state-of-the-art is to use a video camera and tracking cardto generate the list of tracked targets and correspondingangles-to-targets, flood illuminate the FOV and simultaneously detectthe reflected laser energy off of all of the targets in the FOV with animaging detector. Flood illumination provides an active image of all ofthe targets in the FOV. This image may be correlated to the trackedtargets and processed to compute the range to each of the targets. TheSWaP-C of the laser to flood illuminate a FOV and the complexity of theprocessing to extract the range information and correlate it to thetracked targets is burdensome.

SUMMARY OF THE INVENTION

The following is a summary of the invention in order to provide a basicunderstanding of some aspects of the invention. This summary is notintended to identify key or critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts of the invention in a simplified form as a prelude to themore detailed description and the defining claims that are presentedlater.

The present invention provides non-mechanical beam steering that iscapable of illuminating multiple tracked targets per frame one target ata time for target designation, range finding or active imaging over awide FOV.

In an embodiment, a multiple target tracker and beam steerer comprises avideo camera configured to acquire video images of a scene within a FOVwithin a frame time and a video tracker configured to process the videoimages within at least a cue-box within the FOV and output a list oftracked targets and corresponding angles-to-targets within the frametime. A laser is configured to produce a laser spot-beam, typicallypulsed. A liquid crystal waveguide (LCWG) is responsive to commandsignals to steer the laser spot-beam over at least the entire cue-box.One or more processors are configured to process the list of trackedtargets and corresponding angles-to-targets and generate command signalsfor the LCWG to steer the spot-beam to corresponding angles-to-targetsto illuminate multiple tracked targets per frame one tracked target at atime. In different embodiments, the laser beam may be steered toilluminate each of the tracked targets on the list per frame or may besteered to illuminate all of the tracked targets on the list within aspecified number of frames.

In different embodiments the LCWG's steering rate and angular range mustbe fast and wide enough to steer the laser beam over at least the cuebox (and preferably the FOV) to designate a maximum of n targets with atleast one pulse (and preferably at least two) per illuminated target.For range finding and active illumination, the greater the number ofpulses on target, the more accurate the range estimate or the higher theSNR of the active image. For laser designation, the designation code mayrequire a certain number of pulses. This may, for example, limit thenumber of designated targets per frame to maintain the proper pulsecoding. Current LCWG technology has demonstrated steering speeds of upto 1°/μsec over a steering range of at least 35°×8°. For typicaltargeting environments, a steering rate of 1°/msec may suffice. Apolarization grating stack may be used to extend the range to, forexample, at least 50°×50° without a loss of system resolution within theexpanded angular range.

In different embodiments, the ability to discretely and rapidly steerthe laser beam with the LCWG enables prioritization of tracked targetsto vary the revisit rate (e.g., every Nth frame) or dwell time (e.g.,the number of pulses for a specific target within a single frame) for atracked target. The revisit rate determines how often the tracked targetis illuminated while the dwell time determines how many pulses perilluminated target. Prioritization may be based on the range-to-target,heading of the target or location of the tracked target within thecue-box, other target information (e.g., target identification) or acombination thereof. This provides great flexibility for illuminatingtargets in a multi-target environment.

In an embodiment, a user interface accepts commands from an operator toselect a mode of operation (Designation, Range Finding, Active Imagingor a combination thereof). The user interface may also be configured toaccept operator commands to control cue-box size and position within theFOV and target selection. The user interface may also be configured toallow the operator to vary the steering speed of the LCWG to determinethe rate at which tracked targets are illuminated and to set a “keepout” range that determines prioritization.

In different embodiments, a LADAR detector is configured to sensereflected laser energy. The video camera may comprise an out-of-band,in-band or dual-band detector with respect to the spectral band of theLADAR detector. The in-band and dual-band video cameras can be used toprovide closed-loop adjustments to the command signals to steer theLCWG. Each configuration may be used for target designation and rangefinding. For in-band and dual-band video cameras, the video camera maysense the reflected laser energy for active imaging. The in-band videocamera or in-band portion of the dual-band camera may be used as theLADAR detector by combining the LADAR signal processing with the videoprocessing.

These and other features and advantages of the invention will beapparent to those skilled in the art from the following detaileddescription of preferred embodiments, taken together with theaccompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a multiple target tracker and laser beam steererconfigured to track and sequentially illuminate multiple targets perframe within a FOV;

FIG. 2 is a timing diagram illustrating a notional sequence for thetracking and laser illumination of multiple targets per frame;

FIG. 3 is a diagram of an embodiment of a multiple target tracker andbeam steerer in which illumination is prioritized by range-to-target;

FIG. 4 is a timing diagram illustrating a notional sequence for thetracking and laser illumination of multiple targets per frame;

FIG. 5 is a diagram of a user interface and display for the multipletarget tracker and beam steerer;

FIG. 6 is a block diagram of an embodiment of the multiple targettracker and beam steerer using an out-of-band video camera for tracking;

FIGS. 7a, 7b and 7c are top, front and side views of an embodiment of aLCWG configured for laser beam steering;

FIG. 8 is a block diagram of an embodiment of the multiple targettracker and beam steerer using an in-band video camera providingclosed-loop steering control;

FIG. 9 is a block diagram of an embodiment of the multiple targettracker and beam steerer using a dual-band video camera providingclosed-loop steering control and dual-band target tracking; and

FIG. 10 is a diagram of a closed-loop tracking algorithm that tracks thelocations of the tracked target and illumination on the target to steerthe laser to more precisely illuminate the target.

DETAILED DESCRIPTION OF THE INVENTION

The present invention describes a multiple target tracker and beamsteerer that utilizes a liquid crystal waveguide (LCWG) beam steering todesignate multiple tracked targets per frame time one target at a timefor target designation, range finding or active imaging. The steeringrate and range as well as discrete steering capability afforded by theLCWG supports various tracker configurations (out-of-band, in-band ordual-band video cameras), LADAR detectors (single pixel or focal planearray) and prioritization of tracked targets to vary the revisit rate(every Nth frame) or dwell time (within a single frame) for anilluminated target. The LCWG can be used to steer a pulsed or continuouswave (CW) beam. A user interface accepts commands from an operator toselect a designation, range finding or active Imaging mode, controlcue-box size and position within the FOV and target selection. Thereflected laser energy may be detected and processed to computerange-to-target and/or a higher SNR image of the target to augment thevideo display. Alternately, a remote friendly third party may detect thereflected laser energy for the designated target.

Referring now to FIGS. 1 and 2, an embodiment of a multiple targettracker and beam steerer (“tracker/beam steerer”) 100 for Designation,Range Finding or Active Imaging acquires video images of a scene withina FOV 102 at a frame rate (e.g., 30 Hz) that defines a frame time,processes the video images within at least a cue-box 104 (e.g., a circleor rectangle) within the FOV and outputs a list 106 of tracked targetsT1, T2, T3, . . . 108 and corresponding angles-to-targets within theframe time. The size of cue-box 104 is typically set as a percentage ofthe FOV 102. The tracker is typically limited to outputting a maximumnumber of “n” tracked targets on the list. The tracker/beam steerer 100is suitably mounted on a mechanical gimbal 110 to point its boresightaxis 112 in a particular direction e.g., at a selected one of thetargets 108. However, the mechanical gimbal 110 is not required foroperation of the tracker/beam steerer system.

Tracker/beam steerer 100 produces a pulsed laser spot-beam 114 with acertain PRF, whose spectral band may or may not overlap the spectralband of the passively acquired video images. The tracker/beam steerer100 processes the list of tracked targets and correspondingangles-to-targets and generates command signals to steer the pulsedlaser spot-beam to the corresponding angles-to-targets using, at leastin part, liquid crystal waveguide (LCWG) technology, to illuminatemultiple tracked targets per frame one target at a time. Thetracker/beam steerer 100 generates the command signals to set therevisit rate (e.g., every Nth frame) and dwell time (e.g., the number ofpulses per target per frame) of each target based on targetprioritization. The steering range, at least 35°×8°, and steering rate,at least 1 degree per millisecond, and discrete steering controlafforded by LCWG allows for multiple and sequential target tracking perframe over a wide FOV. A sufficient number of pulses can be placed ontarget to enable target designation, or to improve the accuracy of therange estimate or increase the SNR of the active image.

The ability to steer the laser beam discretely, quickly and finely overa large steering range greatly expands the trade-space for designing thetracker/beam steerer for designation, range finding or active imagingapplications. The minimum steering speed may be defined as the productof the required steering range, maximum number of targets, number ofpulses per illuminated target and PRF, and the frame rate. For examplethe minimum steering rate is 1° per millisecond, for a 5.8°×5.8° FOV(8.2° diagonal) where each target is located at extreme corners, amaximum of 5 targets, 10 pulses per target, 100 kHz PRF and a 30 Hzframe rate. For laser designation, the designation code may require alower PRF. This may, for example, limit the number of designated targetsper frame to enable the proper pulse coding. In this mode, steering to 5targets across the 10° FOV takes 32.8 milliseconds, leaving only 0.5milliseconds for designation. The irregular pulse rate for designationmeans the system may have to wait more than 0.5 milliseconds for theproper pulse coding. Switching to only 3 targets per frame enables up to17 milliseconds of spare time to ensure proper designation codes.

As illustrated in FIGS. 1 and 2, 5 targets T1, T2, T3, T4 and T5 arepositioned in the FOV 102 of tracker/beam steerer 100. Tracker/beamsteerer 100 tracks and outputs the list of tracked targets for anytarget that was acquired in the cue-box 104. Targets T1, T2 and T4 arecurrently positioned inside cue-box 104. Target T3 was acquired in thecue-box in a previous frame but has left the cue-box. Target T5 has notbeen acquired (e.g., sensed by the camera and corresponding target dataentered into the video/beam steering processing functions). In thisexample, prioritization is determined such that tracked targetscurrently within the cue-box are revisited every frame and trackedtargets outside the cue-box are revisited every Nth frame. In every Nthframe, the dwell time of a tracked target in the cue-box is set at anominal value (e.g., 10 pulses) whereas the dwell time of a primarytracked target along boresight is set at a higher value (e.g., 15pulses) and the dwell time of tracked target outside the cue-box is setat a lower value (e.g., 5 pulses). In the other N−1 frames, the pulsespreviously allocated to those tracked target outside the cue-box may beallocated to the primary target. This is example is merely illustrativeof the capability afforded by LCWG beam steering to prioritize therevisit rates and dwell times of tracked targets based on heading of thetracked target and position within the cue-box.

As illustrated in FIGS. 3 and 4, 4 targets T1, T2, T3 and T4 arepositioned in the FOV 102 of tracker/beam steerer 100. All targets havebeen acquired and are being tracked. In this example, prioritization isdetermined based on range-to-target. The tracker/beam steerer 100enforces a keep out boundary 116, which may be preset, determined by asystem operator or varied based on the targeting environment. Targets T1and T4 that are inside the keep out boundary 116 are revisited everyframe. Targets T2 and T2 that are outside the keep out boundary 116 arerevisited every 4th frame in this example. The dwell times are allocatedequally among the designated targets within a given frame. Again, thisis merely illustrative of the capability afforded by LCWG beam steering.More generally, tracker/beam steerer 100 may assign priority in the formof revisit rates and dwell times based on the angle to target, positionof the target in the cue-box or FOV, range to target or other targetinformation (e.g., target identification) or combinations thereof. Thecapability to sequentially and discretely illuminate multiple trackedtargets within each frame while prioritizing the designation ofindividual targets based on various target driven criteria greatlyenhances multiple target tracking and designation when compared tocurrent “flash” systems.

Referring now to FIG. 5, in an embodiment a multiple target tracker andbeam steerer may include a user interface 500 and display 501. The rawvideo from the tracker/beam steerer may be fed to display 501 anddisplayed to the operator. User interface 500 communicates with display501 via a video processor 502 in the tracker/designator. Video processor502 may generate and overlay information such as Azimuth and Elevationheading along the X and Y axes, respectively, system state, highlightthe target track ID and provide alternate heading information, or othertarget information requested by the user.

User interface 500 includes a number of configurable options that allowthe operator to interact with and control various aspects of themultiple target tracking and beam steering such as mode selection(Designation, Range Finding, Active Imaging or combinations thereof),target selection for boresight tracking with the gimbal, setting thekeep out boundary distance, setting the position and size of the cue-boxand varying the LCWG steering rate among others. In an embodiment, userinterface 500 is a gamepad controller configured for tracking and beamsteering and includes a switch 503 to turn the display on/off, a switch504 to tag highlighted targets to move from cue to tracked status, aswitch 506 to cycle highlighting through tagged targets and a switch 508to untag all targets. User interface 500 includes a “B” switch 510 totoggle through functions such as mode selection, manually steering thelaser, and manually steering the gimbal, an “A” switch 512 to trackhighlighted target using gimbal along camera boresight, a “Y” switch 514to break closed loop track and an X” switch 516 to enable ranging.Switches 518 and 520 provided gamepad enable/disable and LCWG & lasertracking enable/disable, respectively. Joysticks 520 and 522 allowmotion to set the cue box size and position, respectively, and pressingto reset cue box size and position. Four-position d-pad 524 enables upand down to increase and decrease LCWG steering rate and left and rightto toggle through targets. The same or similar functionality may beimplemented in a variety of different physical user interfaces.

Referring now to FIG. 6, an embodiment of an “out-of-band” tracker/beamsteerer 600 tracks and illuminates targets in different spectral bandsto provide target Designation or Range Finding. Target tracker/beamsteerer 600 comprises an out-of-band video camera 602 configured toacquire video images of a scene within a FOV within a frame time and avideo tracker 604 configured to process the video images and output alist of tracked targets and angles-to-targets within the frame time. Alaser 606 is configured to produce a pulsed laser spot-beam 607 at a PRFin a different spectral band. For example, the laser may produce thelaser spot-beam 607 in the short-wave infrared (SWIR) while the videocamera 602 is configured to passively acquire video images in themid-wave infrared (MWIR). A laser beam steering apparatus 608 includinga liquid crystal waveguide (LCWG) 610 is responsive to voltage signalsto discretely steer the laser spot-beam both in-plane and out-of-planeto the corresponding angle-to-target.

A video processor 612 is configured to process the list of trackedtargets, inputs from a user interface 614 such as target selection,cue-box position and size, LCWG steering rate and prioritizationcriteria and generate command signals for the LCWG. Within a given frametime, the command signals dictate which tracked targets are designatedand for how long (e.g., number of pulses per illuminated target). Fromframe-to-frame, the command signals embody the revisit rate for thevarious targets. For laser Designation, the command signals embody thedefined pattern of pulses to form the designation code. Video processor612 may receive the same or similar information from a source externalto the tracker/designator 600.

The command signals are provided to steering control 615 along with thelist of tracked targets (and angles) from video tracker 604, positionfrom a GPS receiver 616 and orientation from an IMU 618. Steeringcontrol 615 produces the voltage signals to drive LCWG 610 to illuminatethe tracked target with one or more pulses one target at a time withinthe frame time.

A LADAR detector 620 is configured to sense reflected laser energy at asampling rate sufficient to detect the one or more pulses thatilluminate the tracked target. LADAR detector 620 may be a single-pixeldetector or a pixelated detector. A single-pixel detector has theadvantages of low SWaP-C, reduced processing and lower noise. Apixelated detector has the advantages of simplified receiver design,larger FOV, and verification of the steered laser beam position forclosed-loop control.

Optics 622 are configured such that detector 620 senses reflected laserenergy over at least the entire cue-box and suitably the entire FOV ofthe video camera. Optics 622 may be shared with video camera 602, inwhich case a beam splitter is used to split the incident light into therespective spectral bands. Optics 622 may provide a zoom capability. Forexample, at great distances the FOV may be narrowed to increase thespatial resolution to facilitate target acquisition. As therange-to-target decreases, the FOV may be widened to facilitate multipletarget tracking and designation.

A signal processor 624 processes the detector response to the reflectedlaser energy to determine range-to-target. The signal processor willtypically operate on the “time of flight” principle by measuring thetime taken for the laser beam to travel to the target and be reflectedback to the range finder. The signal processor determines when thepulsed spot-beam is transmitted either by directly controlling laser 606or by picking off a small amount of the laser output (<1%). With thespeed of the laser light being a known value, and with an accuratemeasurement of the time taken for the laser light to travel to thetarget and back to the range tinder, the range tinder is able tocalculate the distance from the range finder to the target. Othertechniques such as CW or FM modulated. CW may be used to determinerange. The signal processor sends the range-to-target to the videoprocessor 612, which pairs it with the designated target, and sends avideo signal to display 628.

U.S. Pat. No. 8,380,025 entitled “Liquid Crystal Waveguide HavingRefractive Shapes for Dynamically Controlling Light” assigned to VescentPhotonics, Inc., which is hereby incorporated by reference, discloses aLCWG that can be customized to provide rapid and discrete steering overa defined angular range up to ±35°×±8° with current technology. Thepatent discloses a LCWG that is configurable to form and scan a laserspot over a FOR to provide a relative illumination for active sensors. Atime varying voltage is applied to the LCWG to modulate the liquidcrystal material in order to form and position the laser spot accordingto the specified scan pattern. Liquid crystal waveguides dynamicallycontrol the refraction of light. Generally, liquid crystal materials maybe disposed within a waveguide in a cladding proximate or adjacent to acore layer of the waveguide. In one example, effective refractive-indexproperties of portions of the liquid crystal material can be modulatedto form refractive optical component shapes (e.g. planar lenses orplanar prisms) in the cladding that interact with a portion(specifically the evanescent field) of light in the waveguide so as topermit electronic control of the refraction/bending, focusing, ordefocusing of light as it travels through the waveguide.

The shape of the prism components determines the amount of in-planesteering within the LCWG. The prism elements are arranged in a hornconfiguration where multiple smaller apex angle prisms deviate the laserbeam successively where the start of the horn has smaller aperture,larger apex angle prisms and the end of the horn has larger aperture,smaller apex angle prisms. The number of prisms within the horn and apexangle of each prism determines the total LCWG steering angle at maximumdeflection in the plane of the LCWG. The commercially available LCWGhorn electrode configuration produces a 35°×8° FOR from a 1 mm diameterentrance beam.

Steering out of the plane of the LCWG is achieved using a rectangularelectrode that modulates the effective index of refraction of the corein the region above the internal taper. This modulation changes theangle of light exiting the LCWG due to the internal taper and enablesout of plane steering.

In one example, a waveguide may be formed using one or more patterned orshaped electrodes that induce formation of such refractive shapes ofliquid crystal material, or alternatively, an alignment layer may haveone or more regions that define such refractive or lens shapes to induceformation of refractive or lens shapes of the liquid crystal material.The electrodes are positioned within the LCWG and orientated accordingto the shape of the LCWG core such that each electrode modulates theliquid crystal material for a different direction of steering. Inanother example, such refractive shapes of liquid crystal material maybe formed by patterning or shaping a cladding to define a region orcavity to contain liquid crystal material in which the liquid crystalmaterials may interact with the evanescent light. The LCWG controllerincludes command and synchronization electronics that receive a start offrame/row from a ROIC and generate analog drive signals that specify thescan pattern and a drive controller that converts the analog drivesignals to a high frequency, high voltage drive signal applied to theLCWG. These command and synchronization electronics may also synchronizethe pulses from the laser source.

Referring now to FIGS. 7a, 7b and 7c , the waveguide 700 may begenerally rectangular in shape and may include a core 702 having agenerally rectangular cross-section or defining a parallelepiped betweenupper and lower claddings 704 a and 704 b. On the front end 706 of thewaveguide 700, light 708 is introduced into the waveguide core 702 andpropagates along the length of the waveguide 700 to the distal end 710of the waveguide 700. The direction of propagation of light 708 throughthe waveguide 700 is generally along the length of the waveguide 700,and use of embodiments of the present invention permit the in-planesteering angle 712 and out-of-plane steering angle 714. The steering isaltered depending, in part, on the shapes of the upper shaped in-planeelectrode 716 (e.g. a horn electrode formed of prism elements) and upperout-of-plane electrode 718, and the voltages 720 and 722 applied betweenthe electrodes 716 and 718 and the ground plane 724. Although thewaveguide 700 is shown as generally rectangular, it is understood that awaveguide made according to one or more embodiments of the presentinvention could have other shapes such as square, trapezoid,parallelogram, any polygon, or even be diced or scribed so as to haverounded edges producing elliptical, circular, or any curved shape.

In one example, the shaped in-plane electrode 716 may include a tab orextension therefrom 726 which permits the patterned electrode(s) to beelectrically connected to other electrical elements, such as a voltagesource 720 coupled between the shaped in-plane electrode 716 and thelower electrode or plane 714. Alternatively, electrical traces,conductors, vias or other conventional connection types may be utilizedinstead of or with tab 726 to electrically couple shaped in-planeelectrode 716 to other electrical elements.

The steering range of the laser steering apparatus may be increased bypairing the LCWG with a polarization grating (PG) stack, The PG stackprovides relatively coarse steering over a wide range while the LCWGprovides relatively fine steering. See WO 2014/200581 “Non-MechanicalBeam Steering Tracking System” published Dec. 18, 2014 that provides afield-of-regard (FOR) of 120°×120° or more. Embodiments of a stack ofPGs are described in J. Kim, C. Oh, M. J. Escuti, L. Hosting, and S. A.Serati, “Wide-angle, nonmechanical beam steering using thin liquidcrystal polarization gratings,” Advanced Wavefront Control: Methods,Devices, and Applications VI (SPIE, 2008). Also, see co-pending U.S.patent application Ser. No. 14/811,361 entitled “Non-MechanicallySteered High-Power laser Transmitter” filed Jul. 28, 2015, that limitsthe steering range of the LCWG to at most ±2°×±2° in order to amplifythe laser spot-beam over a FOR of ±10°×±10° or more.

Referring now to FIG. 8, an embodiment of an “in-band” tracker/beamsteerer 800 tracks and illuminates targets in the same spectral band(e.g., SWIR or MWIR). The in-band tracker/beam steerer can be used fortarget Designation, Range Finding or Active Imaging. There isconsiderable similarity of the in-band and out-of-band configurations.Accordingly, like reference numbers are used to refer to likecomponents. For clarity and efficiency, only those components andfunctions that differ will be described.

An in-band video camera 802 is configured to acquire video images of ascene within a FOV within a frame time in the same spectral band asLADAR detector 620. Operating in the same band provides multiplepossible advantages. First, the in-band video camera will simultaneouslycapture an image of both the target to be designated and the reflectedlaser energy (ideally the reflected laser energy is aligned with thetarget center). As will be described in conjunction with FIG. 10, anyerror can be used to provide closed-loop steering control of the LCWG.Second, since the reflected laser energy is “in-band” it is sensed bythe video camera to form an active image of the illuminated target aspart of the video image. Imagery obtained via active imaging with alaser will have a higher SNR than imagery passively obtained with thevideo camera. Signal processor 624 is configured to send a timing signalto in-band video camera 802 (or video tracker 604) to identify thoseimages that contain reflected laser energy. Identifying frames thatcontain laser pulses enables the video tracker 604 to maintain track ontargets even with the higher SNR scene.

Referring now to FIG. 9, an embodiment of a “dual-band” tracker/beamsteerer 900 tracks targets in a pair of bands (e.g., SWIR and MWIR) andilluminates targets in in one of the two bands (e.g., SWIR). Thedual-band tracker/beam steerer can be used for target Designation, RangeFinding or Active Imaging. There is considerable similarity of thedual-band and out-of-band configurations. Accordingly, like referencenumbers are used to refer to like components. For clarity andefficiency, only those components and functions that differ will bedescribed.

A dual band video camera 902 is configured to passively acquire videoimages of a scene within a FOV within a frame time in first and secondspectral bands, with the second spectral band being the same spectralband as the LADAR detector 620 (or physically the same detector). Band 1and Band 2 readout integrated circuits (ROICs) 904 and 906 process thefirst and second spectral bands, respectively. The ROICs are typicallyimplemented as an integral part of dual band video camera 902. Operatingin the same band provides the advantages presented for the in-bandconfiguration plus others. The images generated in the first spectralband by the Band 1 ROIC 904 are unaffected the reflected laser energy.In a first mode of operation, the second spectral band (Band 2 ROIC 906)is used only to provide closed-loop steering control. In this case, band2 ROIC 906 does not have to blank the images. In a second mode, thesecond spectral band (Band 2 ROIC 906) is used to provide closed-loopsteering control and dual-band tracking. In this case, band 2 ROIC 906does have to identify those images containing reflected laser energy.

Referring now to FIG. 10, a closed-loop steering control algorithm 1000based on the Proportional-Integral-Derivative (PID) algorithm utilizesthe “in-band” property of the reflected laser energy in the videoimagery. An image is captured by the in-band video camera (or in-bandportion of a dual-band video camera) (step 1002) and sent to the trackerto determine the locations of the targets (step 1004). The tracker sendsat least the size and location of the multiple targets to SteeringControl for processing. Steering Control determines the steering setpoint (step 1005) and applies the steering voltages to the LCWG to steerthe laser spot-beam to the target position. The image of the laserspot-beam is captured, processed to determine the location of theilluminated target (step 1006) and the steering adjustment is computedin the following loop. The difference of the set point (Error T setinitially at constant value) and location of the laser beam is computedusing a first sum 1008. A PID section 1010 determines the constantsrequired to correct steering. The error is summed using a second sum1012. If the number of samples≤the minimum number of samples X 1016,where samples is the number of sampled pulses, the loop continues tomeasure the range. If the error is<=threshold error T 1018, the range ismeasured. Otherwise, if the error is >threshold error T only thesteering adjustment is made at 1006 and the loop repeats. The error mustbe less than T so you can verify the laser beam is pointing to theproper target. If the number of samples is >threshold X 1016, the loopexits. Using the total samples, the average range is computed 1020,reported to the user and video processor 1022 and the target number isincremented 1024 to measure the range to the next target. This entireprocess occurs within a few tens of microseconds.

While several illustrative embodiments of the invention have been shownand described, numerous variations and alternate embodiments will occurto those skilled in the art. Such variations and alternate embodimentsare contemplated, and can be made without departing from the spirit andscope of the invention as defined in the appended claims.

We claim:
 1. A multiple target tracker and laser beam steerer,comprising: a video camera configured to acquire video images of a scenewithin a field-of-view (FOV) within a frame time; a video trackerconfigured to process the video images within at least a cue-box withinthe FOV and output a list of multiple tracked targets and correspondingangles-to-targets within the frame time; a laser configured to transmita laser spot-beam; a solid-state laser beam steering apparatuscomprising a liquid crystal waveguide (LCWG) responsive to commandsignals to steer the laser spot-beam over at least the entire cue-box;and one or more processors configured to process the list of trackedtargets and corresponding angles-to-targets and generate command signalsfor the LCWG to steer the laser spot-beam to correspondingangles-to-targets to illuminate multiple discrete tracked targets perframe one tracked target at a time.
 2. The multiple target tracker andlaser beam steerer of claim 1, wherein the LCWG is capable of steeringthe spot-beam over a steering range of at least 35°×8° at a steeringrate of at least 1 degree per micro second.
 3. The multiple targettracker and laser beam steerer of claim 1, wherein the video trackeroutputs the list including a maximum of n tracked targets, wherein theone or more processors generate command signals for the LCWG to steerthe laser spot-beam to illuminate each of the multiple tracked targetson the list per frame one tracked target at a time.
 4. The multipletarget tracker and laser beam steerer of claim 1, wherein the videotracker outputs the list including a maximum of n tracked targets,wherein the one or more processors generate command signals for the LCWGto steer the laser spot-beam to illuminate all of the multiple trackedtargets on the list within a specified maximum number of frames onetracked target at a time.
 5. The multiple target tracker and laser beamsteerer of claim 1, wherein the video tracker continues to track targetsthat leave the cue-box, wherein said LCWG steers the spot-beam todesignate targets that leave the cue-box within a steering range of thelaser beam steering apparatus and FOV of the video camera.
 6. Themultiple target tracker and laser beam steerer of claim 1, wherein theone or more processors are configured to prioritize tracked targets andto generate the command signals to steer the laser spot-beam to vary therevisit rate for a tracked target to every Nth frame or a dwell time toilluminate the tracked target with the frame based on its priority. 7.The multiple target tracker and laser beam steerer of claim 6, whereinthe one or more processors are configured to prioritize tracked targetsbased on one or more of the range to tracked target, heading of thetracked target or location of the tracked target within the cue-box. 8.The multiple target tracker and laser beam steerer of claim 1, furthercomprising: a user interface configured to allow a user to perform oneor more of (1) increase or decrease the steering speed to determine therate at which tracked targets are illuminated, (2) toggle throughtracked targets and select a target to point the video camera at theselected target, (3) set the size and position of the cue-box to forcethe video tracker to cue on a target, (4) set a minimum range wherebytracked targets inside the minimum range are prioritized, (5) select amode from Designation, Range Finding and Active Imaging or a combinationthereof.
 9. The multiple target tracker and laser beam steerer of claim1, wherein the laser spot beam comprises a pulsed laser spot-beam with apulse repetition rate (PRF) in which a defined pattern of pulses form adesignation code.
 10. The multiple target tracker and laser beam steererof claim 9, wherein said one or more processors are configured togenerate command signals for the LCWG to synchronize steering of thepulsed laser spot-beam with the transmission of the defined pattern ofpulses to illuminate each of the multiple tracked targets with at leastone defined pattern of pulses.
 11. The multiple target tracker and laserbeam steerer of claim 1, wherein the video camera senses reflected laserenergy to generate an active image of the illuminated targets.
 12. Themultiple target tracker and laser beam steerer of claim 1, furthercomprising a detector configured to sense reflected laser energy over atleast the entire cue-box, wherein the one or more processors process thesensed reflected laser energy to produce a range estimate for each ofthe multiple illuminated targets per frame one tracked target at a time.13. The multiple target tracker and laser beam steerer of claim 12,wherein the detector is a single pixel detector.
 14. A multiple targettracker and beam steerer, comprising: a video display; a video cameraconfigured to acquire video images of a scene within a FOV within aframe time and display the video images on the video display; a videotracker configured to process the video images within at least a cue-boxwithin the FOV and output a list of tracked targets and correspondingangles-to-targets within the frame time; a laser configured to transmita pulsed laser spot-beam at a single wavelength with a pulse repetitionfrequency (PRF); a solid-state laser steering apparatus comprising aliquid crystal waveguide (LCWG) responsive to command signals capable ofdiscretely steering the spot-beam over a range of at least 35°×8° at arate of at least 1 degree per millisecond; one or more processorsconfigured to process the list of tracked targets and correspondingangles-to-targets and generate command signals for the LCWG to steer thespot-beam to corresponding angles-to-targets to illuminate multiplediscrete tracked targets per frame one tracked target at a time; adetector configured to sense at least one pulse of reflected laserenergy over at least the entire cue-box per illuminated target perframe; a user interface configured to accept commands from the operatorfor at least mode selection from Designation, Range Finding and Activeillumination modes, wherein in Designation mode, said laser isconfigured to transmit a defined pattern of pulses to form a designationcode, said command signals generated to synchronize steering of thespot-beam to illuminate each of the multiple tracked targets to receivethe proper pulse within the defined pattern of pulses per frame; whereinin Range Finding mode, said command signals generated to synchronizesteering of the spot-beam to illuminate each of the multiple trackedtargets with at least one pulse per frame, said one or more processorsconfigured to produce a range estimate for each of the illuminatedtargets; and wherein in Active Imaging mode, said command signalsgenerated to synchronize steering of the spot-beam to illuminate each ofthe multiple tracked targets with at least one pulse per frame, saidvideo images including an active image of the illuminated targets. 15.The multiple target tracker and beam steerer of claim 14, wherein theone or more processors are configured to prioritize tracked targets andto generate the command signals to steer the laser spot-beam to vary therevisit rate for a tracked target or a dwell time to illuminate thetracked target based on its priority.
 16. The multiple target trackerand laser beam steerer of claim 14, wherein the video tracker continuesto track targets that leave the cue-box, wherein said LCWG steers thespot-beam to designate targets that leave the cue-box within a steeringrange of the laser beam steering apparatus and FOV of the video camera.17. The multiple target tracker and laser beam steerer of claim 14,wherein the one or more processors are configured to prioritize trackedtargets based on one or more of the range to tracked target, heading ofthe tracked target or location of the tracked target within the cue-boxand to generate the command signals to steer the laser spot-beam to varythe revisit rate for a tracked target to every Nth frame or a dwell timeto illuminate the tracked target with the frame based on its priority.18. The multiple target tracker and laser beam steerer of claim 14,wherein the one or more processors are configured to prioritize trackedtargets and to generate the command signals to steer the laser spot-beamto vary the revisit rate for a tracked target to every Nth frame or adwell time to illuminate the tracked target with the frame based on itspriority.
 19. The multiple target tracker and laser beam steerer ofclaim 14, wherein the laser spot beam comprises a pulsed laser spot-beamwith a pulse repetition rate (PRF) in which a defined pattern of pulsesform a designation code.
 20. The multiple target tracker and laser beamsteerer of claim 19, wherein said one or more processors are configuredto generate command signals for the LCWG to synchronize steering of thepulsed laser spot-beam with the transmission of the defined pattern ofpulses to illuminate each of the multiple tracked targets with at leastone defined pattern of pulses.